Pam, I am so sorry you're feeling blue. I know that feeling of uselessness and valuelessness. It's a crappy place. I'm so sorry you're there.
I don't know you very well, but, for me, what you said is not true. I would miss you if you didn't post. Your posts are thoughtful and reassuring. They have value to me.
I want to recommend a book to you which really changed my life. It's "Loving What Is" by Byron Katie. I think you may know that I'm a life coach and I use Katie's work almost everyday with clients, and with myself. It can really help you see your life in a different way, and I hope you get her book or the book-on-tape, which I understand is quite wonderful.
If I can help you in any other way, know I'm here.